1. Field of the Invention
The present invention relates to novel aqueous colloidal dispersions of a cerium (IV) compound having high cerium concentrations and to a process for the preparation thereof.
2. Description of the Prior Art
It is known to this art from Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition, Vol. 4, p 850, that it is possible to prepare a hydrated ceric dioxide of the Formula CeO.sub.2 .multidot.x H.sub.2 O, wherein x is a number ranging from 0.5 to 2, the compound being present in the form of a gelatinous precipitate, by the addition of ammonium or sodium hydroxide to solutions of ceric salts.
French Patent No. 2,482,075 describes preparation of a cerium (IV) compound dispersible in water by dispersing an essentially dry hydrate of cerium (IV) oxide in an aqueous medium, said oxide having been heat treated at a temperature of from 200.degree. C. to 450.degree. C. in the presence of a deaggregating agent, in particular nitric acid. In this manner, heating in the presence of the deaggregating agent effects disintegration of the aggregated crystallites in the hydrate of cerium (IV) oxide, thereby producing a cerium compound that is dispersible in water.
It is noted in the '075 patent that the preparation of the hydrate of cerium (IV) oxide may be by precipitation from a cerium salt; thus, for example, a high purity cerous carbonate may be dissolved in a solution of nitric or hydrochloric acid in order to provide a neutral solution of cerous nitrate or chloride, which is oxidized with HN.sub.4 OH/H.sub.2 O.sub.2 to produce the hydrate of cerium (IV) oxide
In this prior art process, dispersions of coarse colloids of the hydrate of cerium (IV) are produced, said coarse colloids having particle sizes greater than 500 .ANG..